Optical apparatus for checking the distance between two points on an object and method for measuring small distances



June 20, 1967 J. DYSON ET AL 3,326,079

OPTICAL APPARATUS FOR CHECKING THE DISTANCE BETWEEN TWO POINTS ON ANOBJECT AND METHOD FOR MEASURING SMALL DISTANCES Original Filed May 25,1962 United States Patent 3,326,079 OPTICAL APPARATUS FOR CHECKING THEDISTANCE BETWEEN TWO POINTS ON AN OBJECT AND METHOD FOR MEASURING SMALLDISTANCES James Dyson, Tilehurst, Reading, and Peter John WellesleyNoble, Reading, England, assignors to Associated Electrical IndustriesLimited, London, England, a British company Continuation of applicationSet. No. 197,780, May 25, 1962. This application May 6, 1966, Ser. No.548,018 Claims priority, application Great Britain, May 30, 1961,19,500/ 61 7 Claims. (Cl. 8814) The present invention relates to opticalapparatus and in particular to optical apparatus for checking thedistance between two points on an object. The present invention alsorelates to a method for checking the distance between points on anobject.

The present application is a continuation of our previous applicationSer. No. 197,780, filed May 25, 1962.

It is known to measure small distances between points on an object byforming two images of the object and moving these two images relative toeach other until one image of one point coincides with the other imageof the other point. The two images will then have been moved through adistance equal to the distance between the two points. If the two pointsare located at diametrically opposite positions on the object thedistance will represent the width of the object. Hence such a method canbe used to measure the width of the diameter of an object, for example.

It may be desirable to determine whether the distance between points ona plurality of objects or the diameters of a plurality of objects liebetween certain limits. This problem would arise for example in thecomparison of a plurality of nearly identical objects, as duringinspection in a factory or in the counting of a plurality of particles,for example dust particles, lying between fixed limits of size.Apparatus is therefore required in the form of a G0 or No Go gauge forchecking distances between points on an object or the width of theobject. These distances or widths are small.

The object of the present invention is to provide optical apparatus forchecking small distances between two points on an object.

Another object of the present invention is to provide a method forchecking small distances between two points on an object.

According to the present invention optical apparatus r for checking thedistance between two points on an object comprises two optical systems,means for passing a beam of light from said object through each of saidoptical systems so as to form two images of said object,

Patented June 20, 1967 ICC of the two points towards each other, andthen the secondary component is oscillated between the selectedpositions. This oscillation will cause the images to oscillate betweentwo selected positions. If the images of the points coincide when theimages are in either of these two selected positions or at some instantwhen the images are moving between the two selected positions, thedistance between the two points lies between selected limits.

The apparatus can therefore be used to check whether the distancesbetween corresponding points on a plurality of objects lie betweencertain limits.

The secondary component can be oscillated between adjustable stops so asto vary the selected positions and the limits described above. Theoscillation can be performed manually or automatically.

In order that the invention may be more readily understood referencewill now be made to the accompanying drawing in which:

FIG. 1 is a side view partly in section of optical apparatus embodyingthe invention; and

FIG. 2 is an end view of the apparatus including a diagram of anassociated electrical circuit.

With reference to the two figures the optical apparatus comprises acontainer 1, which is adapted to fit over the top of a microscope drawtube 2, and includes an eye piece 3 located in an aperture 4. The prismgroups 5, 6 are located within the container 1 and comprise tworhomboidal prisms 7, 8 on one end of each of which are respectivelycemented two right angled prisms 9, 11. The interfaces 12, 13 betweeneach rhomboidal prism and its associated right angled prism are treatedso as to be partially reflecting, for example by partially metallisingthe surfaces of the prisms. The prism groups 5, 6 are located so thattheir principal axes are normally parallel and are capable of rotationrelatively to each other about a vertical axis 14, by any suitablemechanism. Two optically plane parallel glass plates 16, 17 are placedbetween the ends of the two prism groups as illustrated and are capableof being rotated about spindles 18, 19 respectively.

The path of a light beam from an object 15 viewed through the microscopeis shown by the arrowed lines. The beam is partially reflected at theinterface 13 and is divided into two component beams which passrespectively through two optical systems. One of these component beamspasses through the rhomboidal prism 8, which is a primary component ofone optical system and is reflected at the end of this prism and passesinto the right angled prism 9, through the interface 12 and into the eyepiece 3. The second component beam passes through the interface 13 andthe right angled prism 11 into the rhomboidal prism 7, which is aprimary com ponent of the other optical system, is internally reflectedtherein and is reflected off the interface 12 into the eye piece 3. Ifthe prisms 7, 8 forming primary components of the optical systems arelocated parallel to one another, the two images of the object formed bythe two component beams will coincide, but if the primary components arerotated relative to one another about the axis 14, the images will moveapart. The images will move in a direction which, for small relativerotation of the prism groups, is normal to the plane of FIG. 1.

Rotation of one or both of the two glass plates 16, 17 which formsecondary components of the optical systems on their respective spindlesabout an axis which is perpendicular to the paths of the two componentbeams will also displace the two images relative to each other by anamount dependent upon the angle through which each glass block isrotated and the thickness and refractive index of each glass block.

In order to check whether the widths of a plurality of particles liewithin certain limits one of these particles is placed in the positionof the object 15 and the two images of the particle formed by theapparatus are moved relative to each other by relative rotation of theprism groups 5, 6, through a predetermined amount from a referenceposition in which the images of the particle coincide. This movementmoves images of diametrically opposite points on said particles towardseach other. Fine adjustment of the position of the images is thenbrought about by rotation of one or both of the glass plates 16, 17. Ifthe glass plates 16, 17 are rotated simul taneously and relativelybetween two fixed angular positions and the corresponding images of thediametrically opposite points on the particle coincide at some instantduring the rotation of the glass plates it will be seen that the widthof the particle lies between fixed limits. Therefore with such anapparatus the widths of a plurality of particles of a similar size canbe checked.

The glass plates 16, 17 can be rotated manually between stops such asthose illustrated in the arrangement in FIGURE 2. In this arrangement anarm 21 is attached to the spindle 19 and is free to move between a fixedstop 22 on the casing 1 and a moveable stop 23, the position of which iscontrolled by a micrometer 24. By altering the setting of the micrometer24 the angular rotation of the plate 17 can be accurately controlled.

The rotation of the spindle 19 may be controlled by the electricalsystem illustrated. This system comprises two electromagnets 25, 26,associated respectively with yokes 27, 28. When either of these magnetsis energised it attracts the arm 21 and therefore the arm 21 movesagainst either of the stops 22, 23. By energising each magnet 25, 26,alternately the arm 21 can be caused to oscillate.

By repeatedly oscillating the arm 21 between fixed stops the diameter ofa plurality of particles can be readily checked. Preferably theoscillation of the arm is such that the plate 17 spends most of its timein its two extreme positions and takes only a short time for the passagebetween these two positions. It will be appreciated that plate 16 iscontrolled by a similar arrangement if it is required to move.

An electrical circuit for providing the correct form of oscillation inthe arm 21 is illustrated in FIG. 2. The circuit comprises two fixedresistances R1, R2, two variable resistances R3, R4, two capacitancesC1, C2 and two transistors T1, T2 connected as illustrated between twosupply lines L1, L2. Typical value of the components are as follows, R1,R24.7 kilohms, R3, R450 kilohms, and C1, C2-25 microfarads. With coilsof resistance 1700 ohms for each electromagnet 25, 26 and a potential of24 volts between the lines L1, L2, and the component values above, thefrequency of oscillation of the plate 17 can be between cycles and ahalf a cycle per second.

When the plate 17 is not required to oscillate the arm 21 may be biasedagainst the moveable stop 23 by a suitable spring.

There is provided by the apparatus described above means for checkingthe small distances between corresponding pairs of points on a pluralityof particles or for checking the diameters or the widths of theparticles.

We claim:

1. In a microscope optical apparatus for indicating small distances onan object comprising means for split ting an image carrying beam alongtwo paths, a means for recombining the beams in the two paths so thatboth beam images are visible in a single eyepiece of the apparatus, anda first beam deflecting means in at least one of said paths arranged foradjusting the relative positioning of the two images visible in thesingle eyepiece, the improvement comprising; a second beam deflectingmeans in at least one of said two paths for further varying the relativepositioning of the two images visible in the single eyepiece, saidsecond beam deflecting means including a deflecting member oscillatablebetween two end positions corresponding to the limits of a predeterminedmeasured distance on the object, means for oscillating the deflectingmember between said end positions, and a means for controlling theamplitude of the oscillations of the oscillatable member between saidend positions.

2. A microscope optical apparatus as claimed in claim 1 wherein themeans for splitting and the means for recombining the two imagescomprise relatively rotatable beam splitting and combining prisms forforming and joining the two beam paths, and the said deflecting memberincludes a transparent parallel plate pivotally mounted transversely tothe beam in at least one of said two beam paths.

3. Optical apparatus for checking the distance between two points on anobject comprising two optical systems, each optical system includingcomponents for forming an image of the same object together with aprimary beam deflecting component and a secondary beam deflectingcomponent controlling the position of the path of the beam of light fromthe object to the image, means for moving the primary deflecting membersof said optical systems relative to each other predetermined amountsfrom reference positions in which said images coincide, the improvementcomprising a means for oscillating the secondary deflecting member of atleast one of said optical systems between two end positionscorresponding to the limits of a measured distance on the object, and ameans for controlling the amplitude of oscillation of the secondarydeflecting member between said end positions.

4. A microscope optical apparatus as claimed in claim 3 including amagnetizable member attached to the said secondary beam deflectingcomponent of one of said optical systems and free to pivot about a fixedaxis, means for limiting the rotational movement of said magnetizablemember, two electromagnets located respectively on opposite sides ofsaid magnetizable member, and means for energizing said electromagnetsalternately so as to oscillate said magnetizable member between itslimits of movement and said secondary beam deflecting component betweenthe said end positions and thereby to oscillate said images relative toeach other between two selected positions.

5. A microscope optical apparatus as claimed in claim 3 wherein themeans for oscillating includes a means for simultaneously oscillatingthe secondary deflecting component of each said system between the saidend positions, and the said means for controlling includes a means forcontrolling the amplitude of oscillation of both secondary beamdeflecting members.

6. A microscope optical apparatus as claimed in claim 5 including amagnetizable member attached to each of said secondary beam deflectingcomponents, each magnetizable member being free to pivot about a fixedaxis, and means for limiting the rotational movement of saidmagnetizable members, two electromagnets located respectively onopposite sides of each magnetizable member, and means for energizing theelectromagnets associated with each magnetizable member alternately soas to oscillate each magnetizable member between its limits of movementand said secondary beam deflecting components between the said endpositions and thereby to oscillate said images relative to each otherbetween two selected positions.

7. A method for checking the distance between two points on an objectcomprising the steps of; splitting an image carrying beam from theobject into two paths, recombining the beams at a later point in saidpaths so that the images become substantially coincident, deflecting oneof said beams to separate the substantially coincident images by a fixedpredetermined amount, which amount is dependent upon the distancebetween said points on the object, and subsequently oscillating at leastone of said separated images so that it moves through a cycle of apreselected amplitude relative to the other image to provide coincidenceof said points at some time during said oscillating, and utilizing saidcoincidence of said points to check the distance between said twopoints.

No references cited.

JEWELL H. PEDERSEN, Primary Examiner.

R. L. WIBEPT, Assistant Examiner.

1. IN A MICROSCOPE OPTICAL APPARATUS FOR INDICATING SMALL DISTANCES ONAN OBJECT COMPRISING MEANS FOR SPLITTING AN IMAGE CARRYING BEAM ALONGTWO PATHS, A MEANS FOR RECOMBINING THE BEAMS IN THE TWO PATHS SO THATBOTH BEAM IMAGES ARE VISIBLE IN A SINGLE EYEPIECE OF THE APPARATUS, ANDA FIRST BEAM DEFLECTING MEANS IN AT LEAST ONE OF SAID PATHS ARRANGED FORADJUSTING THE RELATIVE POSITIONING OF THE TWO IMAGES VISIBLE IN THESINGLE EYEPIECE, THE IMPROVEMENT COMPRISING; A SECOND BEAM DEFLECTINGMEANS IN AT LEAST ONE OF SAID TWO PATHS FOR FURTHER VARYING THE RELATIVEPOSITIONING OF THE TWO IMAGES VISIBLE IN THE SINGLE EYEPIECE, SAIDSECOND BEAM DEFLECTING MEANS INCLUDING A DEFLECTING MEMBER OSCILLATABLEBETWEEN TWO END POSITIONS CORRESPONDING TO THE LIMITS OF A PREDETERMINEDMEASURED DISTANCE ON THE OBJECT, MEANS FOR OSCILLATING THE DEFLECTINGMEMBER BETWEEN SAID END POSITIONS, AND A MEANS FOR CONTROLLING THEAMPLITUDE OF THE OSCILLATIONS OF THE OSCILLATABLE MEMBER BETWEEN SAIDEND POSITIONS.